1. Field of the Invention
The present invention relates to a precision measurement voltage transducer or converter of high accuracy based on a transformer and a servo amplifier.
2. Brief Description of the Background of the Invention Including Prior Art
Measurement voltage transducers are used for example in testing stations for electricity meters, watt meters, voltage meters, test counters, test scoring machines, and other precision apparatus. Such a measurement voltage transducer or converter is known for example from the British Document GB-OS No. 2,034,998A. The output of the amplifier employed according to the reference is on the one hand connected via a transformer winding to ground and on the other hand via another transformer winding and a resistor fed back to the inverting input of the amplifier.
In the case where transformers are employed the errors introduced by measurement voltage transducers depend strongly on the magnetic material employed, that is on the lamination of the transformer. This dependency is avoided in the British Document by having the decisive windings of the transformer carry no substantial current such that the copper resistance and the leakage stray induction does not become effective. This requires the presence of a magnetization winding on the transformer, which excited the transformer core such that the required internal voltage appears at a feedback winding generating a negative feedback. However, no substantial current flows in the feedback winding, since it is loaded with the high resistance input resistor of an amplifier. An active compensation, that is an automatic control, takes care that this internal voltage is adjusted such that a reference alternating voltage supplying the measurement voltage transducer appears at the terminals of the feedback winding. This construction provides the advantage that the magnetizing power does not have to be supplied completely by the servo amplifier, but that the main part is provided by the reference voltage source and only a small part of at most 1 percent is to be produced by the servo amplifier. This results in the advantage that the servo amplifier and its power supply do not have to be dimensioned too large and that the amplification can be smaller with the same quality result and that the "offset" voltage, which can easily lead to saturation of the transformer core, can be controlled in a better way.